Please be aware, the Krungsri ATM cards is not accepted in Hong Kong or Mainland China for cash withdrawals in HSBC or Hang Seng ATM's. Transactions just cancelled without any clear explanation. The same ATM cards works w/o problems in Standard Chartered (both HK/Mainland) and China Construction Bank. I saw such behaviour at least 3 times in the last year.

Maybe this happens, because HSBC sold his Thailand business to Krungsri then for some reason decline all transactions from Krungsri ATM cards.

I very much doubt the reason given above.

Yea, me too. I expect it's a card network issue. I see Krungsri cards use the Visa Plus network for cash withdrawals in other countries. Unless the ATM being used has the Visa Plus logo then the card wouldn't work.

Yea, me too. I expect it's a card network issue. I see Krungsri cards use the Visa Plus network for cash withdrawals in other countries. Unless the ATM being used has the Visa Plus logo then the card wouldn't work.

At some point HSBC HK stopped using the Plus payment system and switched to UnionPay exclusively for their own cards. This caused chaos and eventually HSBC said they were moving back to accepting the Plus system so that their cards could be used overseas. In reverse Krungsri should now be OK for usage. The OP does not say when the refusal was last reported so it may be old news. Or it may be that some ATMs are not reset?